Conventionally, piezoelectric microphones and piezoelectric sounding bodies using a piezoelectric element of a bimorph type have been widely used. A piezoelectric element of the bimorph type is obtained by joining two piezoelectric ceramic substrates together. Alternatively, a piezoelectric element of the bimorph type is obtained by integrally sintering a laminate in which two piezoelectric ceramic layers are laminated.
In order to omit the step of attaching or integral sintering, Japanese Patent Application Laid-Open No. 2007-067125 proposes a piezoelectric element of a bimorph type obtained by using a single piezoelectric layer. In the piezoelectric layer, the polarization axis direction of the portion on one main surface side from the central portion in the thickness direction and the polarization axis direction of the portion on the other main surface side from the central portion are opposite to each other.
In Japanese Patent Application Laid-Open No. 2007-067125, polarization is performed by applying an AC voltage from both sides of the piezoelectric layer after electrodes are formed on both main surfaces of the piezoelectric layer. Therefore, it is impossible to control the polarization axis direction of the piezoelectric layer with sufficiently high accuracy.
An object of the present invention is to provide a piezoelectric element of a bimorph type and a method for manufacturing the piezoelectric element, which are capable of making polarization axis directions of adjacent piezoelectric layers opposite to each other with high accuracy without an additional step such as polarization treatment. Another object of the present invention is to provide a piezoelectric microphone and a piezoelectric resonator having the piezoelectric element.